As a clip chain type sheet stretching apparatus, there has heretofore been known a clip chain type sheet stretching apparatus in which a pair of clip chains each formed of clips combined in an endless shape are disposed laterally symmetrically, and which is configured to hold both end portions in a width direction of a sheet (film) by using the clips of these clip chains, and to stretch the sheet, in a traverse direction (TD stretch) with the clip chains running along a pair of guide rails disposed laterally symmetrically. A distance between the pair of guide rails of the clip chain type sheet stretching apparatus is gradually expanded in a portion for stretching the sheet in the traverse direction.
In order to change a transverse stretch ratio (a ratio of a distance between a pair of clips at an entrance of the sheet relative to a distance between the pair of clips, at an exit of the sheet), the conventional clip chain type sheet stretching apparatus is provided with a flexible guide rail in a portion for connecting straight guide rails made of rigid bodies to each other, and changes an intersection angle (a curvature radius of the flexible guide rail) between the straight guide rails by folding or unfolding the flexible guide rails at a supporting point by using a handle or a motor.
With a larger length and a smaller thickness, the flexible guide rail has a higher bending property, and therefore can change the intersection angle between the straight guide rails within a larger angular range. However, with a larger length and a smaller thickness, the flexible guide rail lacks rigidity. Accordingly, there is a risk that the flexible guide rail is deformed by a stretching force applied to the clips (a force to pull the sheet in the width direction) and fails to maintain an ideal shape (an arc shape), whereby the clip chains cannot run smoothly.
Patent Literatures 1 and 2 are cited as patent literatures related to the conventional technique.